Recent studies in both mammalian cells and bacteria have suggested that there may be differences in DNA excision repair of large, bulky chemical adducts and damage caused by ultraviolet radiation (UV). Because these chemicals are prototypic environmental mutagens, carcinogens, and teratogens, it is essential to know more about how DNA damage produced by these agents is repaired. Although the major objective of these studies is to understand more about repair of chemical damage in human cells, the experiments will rely heavily on recent findings on the role of the E. coli uvrA, uvrB, and uvrC gene products in repair (Tang, unpublished). Three major projects are planned. The first is to complete the characterization of the role of uvrA, uvrB and uvrC gene products in the excision repair of three chemicals [N-acetoxy-2-acetylaminofluorene (NA-AAF), 7-bromomethylbenz (a) anthracene, and benzopyrene-diol-epoxide] and ultraviolet radiation. Many of these studies will be based on my observation that uvrC mutants are defective in the rapair of UV damage but are competent to repair damage produced by NA-AAF. A second study is designed to determine if these gene products either singly or in combination will complement permeable xeroderma pigmentosum (XP) cells damaged with either chemicals or ultraviolet radiation. A third objective is to isolate and characterize eukaryotic proteins involved in the repair of chemical and UV damage. Using both a permeable XP complementation system and a phiX174 RFI DNA nicking assay, I will attempt to isolate from human sources proteins with biological properties similar to those of the uvrA, uvrB and uvrC gene products. The result of all of these studies should be a better understanding of the strategies human cells use to repair chemical damage to DNA.